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  #1  
Old 01-06-2017, 03:21 PM
Soundmig Soundmig is offline
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Default op-amp rolling: Forte Model 2 Pre-Amp

Over the last few days I have installed and "broken in" Sparkos Labs SS3601 discrete op amps in place of the stock LT1028 op amps that originally were in the line stage of my Forte Model 2 pre-amp. I decided to do this, because I have owned several very high-end pre-amps and consequently knew that while this was very nice sounding pre-amp it was missing a fair amount of SQ relative to the best out there. I've actually been contemplating this for over a year, but finally took the time to get the op-amp numbers so as to try something different over the holiday week.

To begin the process, I e-mailed Sparkos Labs with the existing op-amp information and requested their recommendation for an "upgrade". To my surprise Andrew Sparks (Sparkos himself) answered my e-mail - recommending the SS3601's. I placed and order and they were delivered in just a couple of days!

While I was hopeful that miniature discrete circuitry might improve the sound vs. a typical op-amp, I was not expecting much change. Boy, was I wrong. These op amps sound quite a bit better. I could go into a lot of detail, but that would probably be boring. What struck me most about the change is that the sound became much more "real" and far more effortless. Instruments and voices have a better defined position in space (imaging), and the soundstage is deeper and more 3D (width and height didn't change much). Bass sounds deeper and has a bit more drive with better pitch definition, and the highs are much sweeter AND more extended. Detail is enhanced, but the sound is also warmer and more inviting- more pleasant to listen to.

On vocals these devices seem to draw out a more clear sense of the chest and nasal sounds which causes the voices to sound more "natural" and organic. Being a brass player I am very pleased that the enhanced detail and warmth also gives brass instruments (as well as woodwinds) a greater sense of the air moving through the instrument and the "body" and resonance that brings as sense of realism. The sense of percussion from hammers hitting Piano strings is better portrayed now. There is also a noticeable decrease in "glare" or edge from piano and all stringed instruments. Drums and percussion also benefit from slightly better dynamics as well as enhanced detail and "body" along with an improvement in "air" and image specificity for locating cymbals, triangles, etc.

Depending on the listener I suppose these improvements would be described as anywhere from slight to significant. Having played in many a symphonic band, orchestra, Jazz band, etc. these changes are highly significant as they portray more of the recorded information and makes everything sound more like they do when listening to them live and un-amplified. More importantly for me, I'm now much happier with my pedantic and old school pre-amp as the Sparkos Labs discrete op-amps have elevated the Forte's performance to much higher (and more musical) level. I plan to replace the op-amps in the phono stage next and will update this afterwards - if anyone is interested. Note: All listening this far has been digital since I've not updated the phono stage op-amps yet.

FYI - I have no affiliation with Sparkos or any other audio company.
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  #2  
Old 01-14-2017, 01:24 AM
Soundmig Soundmig is offline
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Update: I upgraded the op amps in the Phono Stage also - did that yesterday. Suffice it to say that with Vinyl the difference is even more pronounced since the signal has to go through two op amps (phono stage and line stage). Im very impressed with these devices and the significant difference in SQ that they bring (in my Forte model 2 anyway).
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  #3  
Old 03-31-2017, 12:41 AM
auxinput auxinput is offline
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Hey Soundmig. I have a lot of experience with the Sparkos op amps (as well as several other op amps). The Sparkos are an excellent way to get a true Class A circuit in your device. However, they do suck a LOT of power. I see you have four single channel Sparkos (SS3601). It may not be too bad, but you could see a huge improvement by increasing the size of the capacitors in the main power supply. Look to see if you can get something like 2 x 10,000uf (or as large of a capacitor that will fit).

In addition, soldering a Nichicon Muse 47uf + a 0.1uf MKP directly to the power pins of the Sparkos (pins 4 & 7) will give you faster response and better resolution for mids/highs. I use Vishay MKP416 for the 0.1uf (Vishay part # BFC241641004). This give the op amp more localized power to pull from for those immediate transients.
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  #4  
Old 06-20-2018, 05:52 AM
Soundmig Soundmig is offline
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Quote:
Originally Posted by auxinput View Post
Hey Soundmig. I have a lot of experience with the Sparkos op amps (as well as several other op amps). The Sparkos are an excellent way to get a true Class A circuit in your device. However, they do suck a LOT of power. I see you have four single channel Sparkos (SS3601). It may not be too bad, but you could see a huge improvement by increasing the size of the capacitors in the main power supply. Look to see if you can get something like 2 x 10,000uf (or as large of a capacitor that will fit).

In addition, soldering a Nichicon Muse 47uf + a 0.1uf MKP directly to the power pins of the Sparkos (pins 4 & 7) will give you faster response and better resolution for mids/highs. I use Vishay MKP416 for the 0.1uf (Vishay part # BFC241641004). This give the op amp more localized power to pull from for those immediate transients.
Auxinput, I just now noticed your post (only a year and 3 months late!). I'll see what may be able to fit. I'll check to see if the caps supplying power to those pins can be changed also. Thanks for the input :-)
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  #5  
Old 09-28-2018, 03:27 AM
auxinput auxinput is offline
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And here I am about 3 months later! I have since discontinued using Sparkos op amps. I have found that they just push too hard on the "attack" of the waveforms and things become harsh in the upper mids/highs. They are very clean sounding op amps, but in my system they were too much. I suspect they would work great in a warmer system where you need a lot of "attack" on the instrument hits and punches. The Sonic Imagery op amps are highly superior for a more flat response, but they are not boring at all. The Sonic Imagery are like the bipolar Sparkos without the harsh attack. The Burson V6 Vivid are also excellent, and they impart a somewhat organic feel to the mix (since they are FET based devices).
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  #6  
Old 09-28-2018, 06:49 AM
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W9TR W9TR is offline
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Glad to see some op-amp rolling going on! Awesome!

Do you have a 200 MHz Oscilloscope handy or can you borrow one?

The reason I ask is that many times when you roll op-amps you can create a low level high frequency oscillation that’s not detectable by ear or with audio measurement equipment. This is true even for unity gain stable op-amps. It definitely impacts the sound in a lot of unpredictable ways.

Checking to see if your ‘roll’ is clean is an important step in the process.

Tom

P.S. I’m an analog/RF design engineer .
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  #7  
Old 09-28-2018, 10:47 AM
Soundmig Soundmig is offline
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Quote:
Originally Posted by auxinput View Post
And here I am about 3 months later! I have since discontinued using Sparkos op amps. I have found that they just push too hard on the "attack" of the waveforms and things become harsh in the upper mids/highs. They are very clean sounding op amps, but in my system they were too much. I suspect they would work great in a warmer system where you need a lot of "attack" on the instrument hits and punches. The Sonic Imagery op amps are highly superior for a more flat response, but they are not boring at all. The Sonic Imagery are like the bipolar Sparkos without the harsh attack. The Burson V6 Vivid are also excellent, and they impart a somewhat organic feel to the mix (since they are FET based devices).
I've moved my Forte pre-amp down the road in favor of a Schiit Freya, so I'm no longer able to try new op-amps in the Forte. I tend to like FET's, so the Burson V6 would have been very interesting to try! BTW- my favorite operational mode of the Freya is the balanced JFET buffer output mode.
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Old 09-29-2018, 12:14 AM
auxinput auxinput is offline
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W9TR - Sorry, I don't have a scope to measure that. However, I always solder a 47uf electrolytic + a 0.1uf MKP directly across the power pins of the op amp (with the exception of the Burson). This gives an additional mid punch as well as high frequency stabilization. I believe this also helps reduce oscillation from the +/- voltage rails.

Soundmig - if you have a very high resolution system you can view this on, Tyco Dog has posted many videos with tube rolling on the Shiit Freya. I can hear subtle differences between the tubes on my ultra high-resolution computer audio system, but odds are that you may not. The stock tubes that come with Freya aren't that great, in my opinion. Here's the two most important, in my opinion:

https://www.youtube.com/watch?v=z-kQaCdjylc

https://www.youtube.com/watch?v=NtL4jIEgfSc&t=200s


On the first video, the Electro-Harmonix tubes clearly are the fastest and highest resolution. They are actually faster with quicker attack and detail than the stock "JFET solid state mode" of the Freya! The Electro-Harmonix could actually come across as thin sounding on some systems (if you have an amp that is very fast and resolving, such as Bryston).

The Amperex 6SN7 tubes do not have the resolution of the Electro (and I have told many people this), but I just get chills whenever the Amperex comes on. It's very engaging and has a real "analog" sound to it. Many people have posted that Amperex is a magic tube. However, they are very hard to find (if you find a "real" NOS Amperex tube) and are VERY expensive.

On the second video, it's difficult for me to tell, but I think the PSVANE CV181-1 may be close to the fast resolution of the Electro-Harmonix, but I think PSVANE has more body (without the thinness) and will "sing" better. They are definitely expensive. The Shuguang "Treasure" seems nice, but it is darker sounding with rolled off highs. I think PSVANE is probably the best current manufacturer of preamp type tubes today.

They appear to have several "6SN7" type variants:

http://psvanetube.com/wordpress/purc...sn7-aka-cv181/

Don't take my statements as gospel. They are just my impressions by listening. But these are definitely tube-rolling ideas for the Freya (which is basically the same as op amp rolling).
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  #9  
Old 09-29-2018, 11:21 AM
Soundmig Soundmig is offline
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Quote:
Originally Posted by auxinput View Post
W9TR - Sorry, I don't have a scope to measure that. However, I always solder a 47uf electrolytic + a 0.1uf MKP directly across the power pins of the op amp (with the exception of the Burson). This gives an additional mid punch as well as high frequency stabilization. I believe this also helps reduce oscillation from the +/- voltage rails.

Soundmig - if you have a very high resolution system you can view this on, Tyco Dog has posted many videos with tube rolling on the Shiit Freya. I can hear subtle differences between the tubes on my ultra high-resolution computer audio system, but odds are that you may not. The stock tubes that come with Freya aren't that great, in my opinion. Here's the two most important, in my opinion:

https://www.youtube.com/watch?v=z-kQaCdjylc

https://www.youtube.com/watch?v=NtL4jIEgfSc&t=200s


On the first video, the Electro-Harmonix tubes clearly are the fastest and highest resolution. They are actually faster with quicker attack and detail than the stock "JFET solid state mode" of the Freya! The Electro-Harmonix could actually come across as thin sounding on some systems (if you have an amp that is very fast and resolving, such as Bryston).

The Amperex 6SN7 tubes do not have the resolution of the Electro (and I have told many people this), but I just get chills whenever the Amperex comes on. It's very engaging and has a real "analog" sound to it. Many people have posted that Amperex is a magic tube. However, they are very hard to find (if you find a "real" NOS Amperex tube) and are VERY expensive.

On the second video, it's difficult for me to tell, but I think the PSVANE CV181-1 may be close to the fast resolution of the Electro-Harmonix, but I think PSVANE has more body (without the thinness) and will "sing" better. They are definitely expensive. The Shuguang "Treasure" seems nice, but it is darker sounding with rolled off highs. I think PSVANE is probably the best current manufacturer of preamp type tubes today.

They appear to have several "6SN7" type variants:

http://psvanetube.com/wordpress/purc...sn7-aka-cv181/

Don't take my statements as gospel. They are just my impressions by listening. But these are definitely tube-rolling ideas for the Freya (which is basically the same as op amp rolling).
Very interesting. I have the supposed upgrade Tung Sol tubes - which sound very good and (now that they are broken in) very similar to the JFET buffer - just not quite as "open" sounding (subtle - splitting hairs). BTW it took 3 weeks of continuous on time to get those Tung Sol's to settle in. I'm really curious about the Schiit Solid State tubes (LISST) - any videos out there using those? FYI - my listening room doesn't get nearly as hot now that I took the tubes out of the Freya - geez that things runs hot with tubes!!!
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  #10  
Old 09-29-2018, 09:23 PM
auxinput auxinput is offline
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No videos as far as I can find. You can read this long thread if you want. However, the opinions seem all over the place and all of these people are using the LYR or something that doesn't already have JFET:

https://www.head-fi.org/threads/schi...ssions.778326/

There is a statement in there that the LISST definitely warm/heat up, but not as much as tubes. So, a couple things could be happening:

1. The LISST is regulating down the tube high voltage (i.e. 200+ volts) to a more solid state level such as 15-30 volts and generating heat as a byproduct.

2. The LISST MOSFET circuit is running in Class A mode, which generates more heat.

Or it could be both of these. Schiit indicates the LISST are MOSFET circuits, as oppose to JFET that is the solid-state circuit in the Freya. So, it's really difficult to tell if the LISST is going to be any different than the built-in JFET.

Honestly, I think the JFET mode sounds somewhat flat and sterile when compared to good tubes (the Schiit stock tubes are not included). You could always try the LISST, but at $99 a pair, it's an experiment that may or may not be better than stock JFET.

If it were me, I would be going after the PSVANE CV181-TII, even though they are a lot more expensive.
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